Wire brush attachment for angle grinder

ABSTRACT

Accessories for an angle grinder include a rotary disk tool having a working zone around the periphery of the disk comprising a plurality of wire bristles and a rest means for supporting the grinder on a surface to be shaped. The rest means may be a non-rotating nose beneath the grinder, a rubbing contact mounted on a flat tool or simply the central part of a convex tool Tilting the grinder about the rest means gives effective control of the tool. Steeper tilts cause the cutting surface to bite more deeply into the work. The grinder is stroked toward the user with the cutting zone  2206  trailing. Most disks are perforated. Work to be shaped can be seen through the spinning disk during use. A tool base onto which a variety of cutting surfaces can be affixed is also provided, and a type of wire brush attachment incorporating a rubbing contact is provided.

TECHNICAL FIELD OF THE INVENTION

This invention relates to the field of disc-shaped rotating abradingtools of the type having manufactured surfaces for abrading and formingmaterials, and in particular this invention relates to a wire brushaccessory which is adapted for use with a hand-held angle grinder.

BACKGROUND

A number of applications in the construction or repair of solid articlesinvolve the selective removal of material from a bulk in order toproduce a desired conformation or shape. For example a builder mayremove some wood from a beam in order to produce a neat fit—more likelyif the house being built is non-rectangular; a foundry removes surplusmetal from sprues or joints between mould parts when producing acasting; a wood carver selectively removes wood in order to produce acarving; a panel beater frequently removes surplus plastic filler whichwas placed within a defect in an automotive panel to build it up, sothat the outline conforms with the original outline of the panel; or aboat builder may have to remove kilograms of material, such aslead-filled fibreglass when shaping or repairing a hull.

The act of selective removal, particularly if carried out by abrasivemeans, involves the expenditure of considerable effort and abrasivematerials. The work can be quite slow. There is also a number ofproblems and health risks associated with the consequent fine dust,having potentially toxic, carcinogenic, or explosive properties.Moreover, dust containing glass fibre is particularly dangerous to thelungs.

One form of tool used for removal of loosely adhered material is acup-shaped wire brush rotating on a spindle. One such device isdescribed in German OLS 25 02 698.

STATEMENT OF THE INVENTION

In a previous Application published as WO 95/29788 on Nov. 9, 1995,Applicant described an invention in which a first aspect comprised anaccessory for a grinder including a rotatable tool having a shapesubstantially that of a disk, having an axis of rotation and capable ofbeing mounted on an arbor of an angle grinder, characterised in that therotatable tool is provided with at least one working zone within anactive zone extending inwardly from the perimeter of the tool; and restmeans extending substantially inwardly from the working zone of thetool, which rest means is displaced from the working zone along the lineof the axis of rotation. In some cases the working zone is co-extensivewith the active zone.

In a related aspect the previous Aplication comprises an accessory for agrinder characterised in that the rest means is concentric with andsupported on the rotatable tool.

In a related aspect the previous Application comprises an accessory fora grinder characterised in that the rest means comprises a portion of aconvex working surface of the rotatable tool and the rest means includesat least one rubbing surface located between the active zone and theaxis of rotation.

In a related aspect the previous Application comprises an accessory fora grinder characterised in that the rest means comprises a fixed rubbingsurface or nose supported on the angle grinder and displaced so as to besupported beyond the rotatable tool. (By “beyond” we mean beyond the endof the arbor, or below the tool as it is normally held).

In a further related aspect the previous Application comprises anaccessory for a grinder comprising a rotable tool characterised in thatthe working zone comprises at least one area within the active zone ofthe rotatable tool, and the active zone surface extends radially inwardover the working surface from the perimeter for up to two thirds andpreferably one third of the radius of the rotatable tool.

The present invention provides a further extension of the generalconcepts embodied in the previous Application described above. In oneaspect of this extension the invention provides an accessory for agrinder comprising a rotatable disk-shaped tool, having an axis ofrotation and adapted to be mounted on an arbor of an angle grinder, theaccessory being provided with a working zone located on the rotatabledisk-shaped tool and extending inwardly from the perimeter of the tool;and rest means extending substantially inwardly from the working zone ofthe tool, which rest means is located radially inward from the workingzone and displaced by a fixed distance along the line of the axis ofrotation of the tool and away from the grinder, wherein the working zoneof the rotatable tool is provided with a plurality of stiff bristlescapable of performing a cutting or abrading action when in rotationalmotion, the bristles projecting from the surface of the working zone andthe length of the bristles being such that a portion of the rest meanscan be contacted with a work surface without contact occurring betweenthe bristles and the work surface.

In a preferred aspect of the invention at least one viewing aperture isprovided through the disk of the rotatable tool and at least one viewingaperture may, when the tool is rotating, also serve to cause airmovement.

Preferably the grinder has a central recessed mounting aperture providedwith gripping means or clutch means capable of disengagementsubstantially as long as a torque applied between the rotatable spindleand the tool exceeds a predetermined amount and optionally a resilientmounting means capable of reducing vibration.

In use the preferred disk-shaped rotatable abrading tool is mounted on arotatable spindle, and comprises an active zone on said rotatableabrading tool, which active zone comprises a least one working zonecomprising stiff bristles capable of removing material from the worksurface, and rest means (a rest zone) dispaced along the axis ofrotation by a fixed amount from the working zone, which rest means, inuse, permits control of the shaping action of the grinder system byfirst contacting the rest means with the work surface and then tiltingthe grinder system to cause or increase engagement of the bristles inthe working zone with the work surface.

In a further preferred aspect the invention the rest means comprises arubbing surface provided with rotational bearing means, which preferablymoves on the same axis as the disk-shaped tool, so that in use therubbing surface may rotate independently of the rotatable tool.

Preferably at least one viewing aperture is provided through the tooland in which at least one viewing aperture may when the tool is rotatingalso serve as to cause air movement.

The rotatable abrading tool of the invention preferably has a centralmounting aperture adapted for attachment to a rotatable spindle.

Preferably the rotatable tool has a central recessed mounting apertureadapted for attachment to a rotatable spindle and is provided withclutch means capable of disengagement while a torque applied between therotatable spindle and the tool exceeds a predetermined amount.

Preferably the central recessed mounting aperture is also provided withresilient mounting means capable of reducing vibration caused byeccentricity.

Preferably the means for attachment of the tool comprises a shapeddepression, shaped to match the profile of an arbor and nut. Preferablythe nut includes means to impose a grip on the tool using staticfriction, and preferably the static friction is overcome at a torqueless than that which can damage a means for driving the rotary shaft.Preferably the tool is adapted for use with an ordinary angle grinder.Optionally it may be adapted for use with other rotatable poweredmachines. Optionally the angle grinder may be fitted with a guard, inorder to control swarf.

In use the tool of the invention provides a method for shaping material,comprising the steps of (a) causing a tool according to the abovedescription having viewing apertures therein to be affixed to an anglegrinder or the like, (b) applying power to the angle grinder motor, (c)holding the tool against the work while tilted at a low angle to it (sothat the rest means contacts the surface but the working surface is notengaged) and raising the tilt to a higher angle so that the workingsurface contacts the work surface with a controlled pressure, and (d)drawing the tool towards the user meanwhile having the opportunity toview the work through apertures in the rotating tool.

Preferably the tool is adapted for mounting upon the spindle or arbor ofan angle grinder tool and for this purpose the tool is provided with anoptionally threaded central mounting aperture. Optionally the border ofthe central aperture is depressed towards the inner surface of the tool.Preferably the tool is made of mild steel although alternatively it maybe made from a hardenable metal or alloy or from a plastics material.Optionally the tool may be made by other processes, including pressuredie-casting. Preferably a mild steel disk 2 to 6 mm thick provides thebasi of the tool. Optionally the disk may be flat and in this case theremay be two active zones, one on each major surface, although only onecan be used at one time. Preferably the disk is deformed into a conicalor curved profile with at least the active zone of the outer surfacebeing a convex surface.

WIRE BRUSH

It is commonly held that wire brush attachments, even a 3 inch, (7.62cm), diameter cup brush, “kill” angle grinders by imposing high torques.FIG. 2 shows a variety of wire brush disks, in section, suitable for anangle grinder. These are shown as complete disks because the prototype(see FIG. 3) was made in this way. In FIG. 2, the lower version ispreferred over the upper version (for most purposes) because the longerbristles have a longer distance in which to flex and should last longerbefore breaking. Note that in both versions the disk has a central“bare” zone which may be used as a rest zone in accordance with theprinciples of the invention. (3002 and 3004 represent means forattachment to the arbor of an angle grinder).

FIG. 3 shows a face view 3100 of a prototype wire brush disk for anangle grinder. The outer perimeter of the tool is provided with aplurality of stiff bristles or wires capable of performing a cutting orabrading action when spinning at typical angle grinder speeds. For theprototype these were made by manually fitting bristles though holesdrilled in a blade, and gluing them into place after adjusting forlength. In this prototype a number of viewing holes 3101 have been made(also useful for enhancing air movement and possibly their edges arealso useable for cutting) and a number of bristles of a suitable iron orsteel wire have been embedded in the disk towards its periphery, asshown at 2302. A side view of one of the bristled sectors is shown at3104, with protruding bristles 3103. All of the bristles or wires whichmay be made of straight or crinkled (crimped) wire project to a heightwhich is less than that of the rubbing surface. Once again, the tool isused with a kind of tilting action, using the central portion of thetool as a rubbing surface and tilting the angle grinder forwards untilthe bristles are just engaged with the work. In contrast to previouswire brushes for angle grinders, this kind of wire brush does not haveany “kick” if used with tilting, as above. We believe that providing thebristles in sectors, with breaks in between, is beneficial to the actionof the brush, perhaps by giving the work a little cooling time orperhaps by reducing the torque applied to the angle grinder.

The materials from which the bristles are made are preferably steel orother alloys of iron but other extrudable metals such as copper, brass,bronze, tungsten and the like can be used depending on the toughnessrequirements imposed by the intended applications. In some situationsceramic fibers may be substituted for the metal fibers providing thebristles. Suitable ceramic bristles include alumina fibers.

DRAWINGS

The following is a description of a preferred form of the invention,given by way of example

FIG. 1 shows three general optional profiles for the basic tool memberuseful in the present invention (without the bristles).

FIG. 2 shows a variety of wire brush disks for an angle grinder.

FIG. 3 shows a face view of a wire brush disk for an angle grinder.

FIG. 4 shows the method whereby an angle grinder incorporating a toolaccording to the invention, (minus the bristles), is used. The tool isinclined about the rest point in order to engage, or further engage, theactive contact zone with some work material.

FIG. 5 shows a type of guard for a grinder system, including a centralmound or protrusion capable of being used as a rest point, hence bettercontrol of the tool is possible. This type of system is particularlyuseful where the tool is flat.

FIG. 6 shows a type of resilient central mount for a tool according tothe invention.

FIG. 7 shows an alternative clutch and central resilient mount for adisk.

PREFERRED EMBODIMENT THEORY PRINCIPLES

The invention is used primarily as a component of a hand-held grindersystem. As practically all of these are for the type of machine known asan angle grinder we shall predominantly refer to angle grinders. Inaddition the invention will be more particularly described withreference to the above Drawings.

The angle grinder is provided with a rest point, (or rest means),comprising means to lean or rest the tool on the work surface, while inuse, and from that rest point, gradually slope or incline the machineuntil the bristles in the working zone of the tool start abrading thework surface. From this time the grinder may be slid or “stroked”preferably towards the operator. The apertures or viewing holes in thetool permit the surface being treated to be inspected prior to abrading.The rest means can optionally be provided on the body of the anglegrinder; most conveniently as part of a guard beneath a portion of thewheel (FIGS. 4 and 5) or alternatively we can provide that the restmeans is located on the spinning disk, where it may form:

(a) A more central part of the disk—here a domed or convex disk ispreferred (FIG. 1/101),

(b) An attached protrusion such as a domed washer, spinning with thedisk (here the disk itself may be flat though still providing an activezone at one side of its perimeter) or

(c) An attached though separately rotatable protrusion, such as a domedwasher mounted by means of a bearing onto the disk or grinder spindle.This is commonly termed a “dead” guide.

Intimately associated with this method-based concept is the provision ofabrading tools having an active, or working, zone comprising the entireouter perimeter extending inwards by about one third of the radius, oran active zone comprising isolated abrading sites within the entireactive zone, and a rest zone located radially inward of the workingzone.

In more detail, the preferred tool comprises an optionally perforatedmetal disk capable of attachment to the angle grinder shaft. Preferreddisks are convex, like the saucer for a cup, and have an active workingzone with abrading bristles located on or about the convex perimeter.

Because the invention comprises a disk rotated at a high speed itacquires a considerable angular momentum which helps provide a steadyrate of abrasion. In one preferred form, the tool is adapted to be usedwith a conventional angle grinder of the widely used type having atypical no-load rotation speed of 11,000 rpm, driven usually by auniversal (AC/DC) brush motor. Conventional angle grinders provide adrive shaft onto which various discs (normally of abrasive material) maybe mounted and spun at a high speed. A typical angle grinder is thesingle-speed 115 mm grinder sold as the “AEG WSL115” (TM) (600 watts).This size of motor provides an acceptable power for the prototype disks.A variable-speed angle grinder may be an advantage.

In use, the work-material and the working surface of the disk arebrought together so that the work-material approaches the working zonefrom the centre of the disk and the trailing edge of the working zone isthe disk edge. The work at or close to the site of the abrading ispartially visible through holes cut through the disk.

When using an angle grinder with a tool according to this invention, thepreferred movement is to drag the tool towards the user, or stroke itover the work material, while the working zone engages the material. Thepreferred apertures allow the user to see, through the disk, the sitewhere the tool is about to cut or abrade. There is relatively little orno “kick” from the tool (not often the case with ordinary angle grindertools or saw-like modifications), and it is easy to hold and control themachine during operation in order to carry out relatively finemovements.

The angle made by the handle of the angle grinder to the work istypically about 30 degrees, (varied by the user from about 15 degrees toabout 40 degrees) using the example cutter, but this depends on theshape to be formed. The angle allows the effective tooth protrusionamount to be varied. FIG. 4 illustrates this method, (minus the bristlesfor the sake of clarity), in which the rest means is a nose (left sideseries) or a rubbing surface. At the left are three variations (2201,2202 and 2203) of tilt (respective to a work surface 2200) of an anglegrinder with a nose 2205 and a flat disk 2204; wherein the grindersystem is being tilted on its nose 2205 so that the rotating disk 2204approaches the work. In the centre left drawing the disk is justcontacting the work. In the lowest left drawing it has eaten into thework at 2206. At the right of FIG. 4 are shown three angles of tilt of aconvex tool with an annular blade attachment 2207, (minus the bristles),where the rubbing surface 2205 (which in this example is part of therest zone ans also a part of the actual disk) moves towards theperiphery until in the lowest drawing the bristles on the disk, (notshown), are abrading the work surface at 2206. Under full working loadthe disk has a rotation speed of 8,000 rpm, which approximates, for adisc having four distinct working areas in the active zone, (as shownfor example in FIG. 3), 32,000 abrading actions per minute. The operatoruses the sound of the loaded motor as a guide in adjusting the speed ofabrading.

DISK ITSELF

We prefer to provide a dished disk so that we can place the bristles onthe outside or convex side of the disk near its rim, and so allow theuser to vary the abrading pressure by tilting the disk. Disks can becurved in profile, or include a conic section, or in some cases may beflat. At the disk centre we prefer to provide a profile that mates withan arbor though optionally each abrading disk may include a thread fordirect mounting, perhaps with a spacing washer. The conic or curvedprofile can be a separate part of a disk.

We have made prototype tools from mild steel sheet, from 3 to 6 mm inthickness, and from stainless steel, though other materials can be used.The overall diameter is set by the abrading disk guard and generallyranges from about 4 to 4.5 inches (100-112 mm) for a nominally 4.5 inchangle grinder. The first prototype was made by spinning a heated disk ofmild steel on a lathe. Other methods of forming a metal disc includestamping and shaping from sheet stock, or using laser-cutting techniques(particular for hole cutting), then pressing in a die. A abrading diskof a plastics material may be made by the usual techniques such asinjection moulding and optionally these techniques include provision ofa fibrous base or core about which a matrix is formed.

Flat-bladed disks with annular attachments can also be producedaccording to this invention. In order to provide a rest zone or rubbingsurface for use with such a flat disk, a kind of dome nut can be used aspart of the attachment of the disk to the grinder drive shaft. The headof this dome nut is held in rubbing or sliding contact with the work,and the cutter is tilted so that the bristles dig in at a suitable rate.The dome nut may be shaped more like a mushroom, but then the increasedradial velocity of the surface in contact leads to increased friction,wear, and reaction forces.

Optionally, a separately mounted domed spacer may be used. This can be,at least in part, rotationally mounted—for example, on a ball-bearing—sothat it may come to rest rather than rub on the surface of the work, andprovide a rest zone as a non-rubbing surface without friction. In thecase of some plastics (for example), the friction generated by slidingat the rubbing surface (especially at the rates of revolution typical ofangle grinders) may cause local burning, melting, difficulty of control,and damage to the surface. This improvement overcomes that problem.

A further type of rest means is provided on the actual angle grinderitself—not on the surface of its abrading disk. FIG. 5 illustrates ahard “nose” 2101 of for example hardened steel, chromium alloy, or forsome applications a low-friction nose of PTFE plastic(polytetrafluorethane or “Teflon (™)”) which is attached to the centreof a partial guard 2102 attached beneath the abrading disk of an anglegrinder 2103. The beneath view B depicts an aperture 2104 which isintended for the ejection of waste material—swarf and the like. The sideview A shows a flat disk type of abrading disk 2105 which is providedwith bristles, (not shown), presented to the edge 2106. It will beevident that if the nose 2101 is rested on work material, and the bodyof the angle grinder 2107 is tilted so that the “active” edge 2106 ofthe abrading disk comes into contact with the work, an operator has afar better degree of control over rate and depth of abrading than if lieor she has no “nose” or rest means and has to set the active edge in thecorrect position solely by hand positioning.

The guard 2102 may be provided with a hinge and catch mechanism (notshown) so that it can flip open to allow the abrading disk to be cleanedor changed. Part C of this drawing shows an abrading disk 2108 having adished profile and the adjacent nose 2101 and guard 2102. This presentsa more nearly parallel alignment of tooth edges to a sheet of workmaterial and is for example more suited to hand planing. Thismodification to provide a grinder system having rest means is notincompatible with the extra guard 1705 offered in FIG. 17 for the uppersurface of the disk.

DISK HOLES

Perforations in the disk are provided in part so that the user can seethe material to be abraded through the spinning disk as the tool workingzone is drawn towards the user. For convenience the perforations arecircular or at least have no sharp or narrow corners because of the riskof propagation of cracks from stressed areas. Holes 24 mm in diameterhave been suitable. The holes are preferably equidistant from the centrebut this arrangement is not essential. Clearly, hole positions should beselected so as to retain the balance of the disk, and disks may bebalanced dynamically by removing material from hole edges. Theperforations may also aid in stirring the air so that any swarf iscarried by the moving air and is ejected further or more effectively.For moving air the holes may be racked (drilled obliquely) or pitched.They may also be used as clamping points for a jig for alignment of theabrading disk in automated sharpening operations.

Holes are a preferred option for the disks of the invention; providingvisibility of the work about to be abraded, and aiding (especially ifraked) in stirring and moving the air. The preferred embodiment hasthree equally spaced holes. Other combinations which place various holesat different distances from the centre may be used; although it isalways preferable to maintain static and dynamic balance in rapidlyrotating disks.

MOUNTING MEANS

We have provided a central threaded aperture in our prototypes.Generally a spacer or thrust washer of approximately 10 mm thickness isused about the arbor or spindle of the angle grinder, beneath theconcave face of the disk, so that its spinning edges clear the guard ofthe angle grinder; although a suitably pressed abrading disk having adepressed mounting hole may not require the use of a spacer.Conveniently the threaded disk prototypes do not bind onto the anglegrinder during use.

MOUNTING SYSTEM

A further improvement is the use of a flexible or resilient mount,inserted between the arbor of the angle grinder and the material of thedisk - any disk described or illustrated herein. FIG. 6 shows at 1900 aresilient central mount for a wheel 1901, having among other purposesthe objective of minimising the effect of wheel imbalance on toolvibration. In FIG. 6, the resilient material (which is illustrated as1906) is contained within a housing 1904 attached to the wheel, while acentral threaded collar 1907 surrounding an aperture 1902 is attached toa fin 1905 running deeply into the resilient material, which isgenerally a type of rubber. There is a small gap at the base to allowwobble between the housing and the thread at 1903. Optionally the smallgap may be at the outside, and the inner gap may be an interference fit.Optionally there may be a further layer of metal, between (and attachedto) the resilient material and the fin 1905, to which it is not attachedapart from a frictional grip, thereby providing a clutch so that if thetorque exceeds a threshold, the fin 1905 may slip inside the furtherlayer of metal. The base of the threaded collar (by 1907) serves as anut to lock the wheel onto the arbor of the grinder.

We have also designed an alternative mounting system for an anglegrinder. This is illustrated in FIG. 7 which shows at 2400 analternative clutch and central resilient mount to that of FIG. 6 for usewith a tool base or disk. The clutch is designed to allow slippage whenthe torque applied to the tool is greater than a preset amount. It mayinclude a “chatterbox” of some type to give an audible indication ofslippage, and one way of providing this is to place several ballbearings 2402 between the disk and the resilient mount so that the ballsclick into or out recesses if the clutch slips. In this example theportion of the resilient mount threaded onto the arbor of the anglegrinder has a cone-shaped projection (as seen in section 2401) into theresilient material.

ADVANTAGES

Advantages of preferred forms of this invention include

1. Material is removed quickly.

2. There is little reaction or kickback against the tool edge, reducingstresses on operators, and minimising the risk of exhaustion and errorswhich may be expensive and/or dangerous;

3. Control of the results is excellent, achieved by tilting (to vary thebite) and moving the tool over the work surface, while experiencinglittle kickback.

4. The user can see through perforations in the spinning disk toaccurately produce a desired conformation, or shape;

5. The material of the disk need not be high-quality steel as is thecase for circular saw blades, for example.

6. The work applied to the tool (ie. the power consumption of thegrinder) is usually low enough to enable a rechargeable battery-operatedgrinder to be used.

Finally, it will be appreciated that various alterations andmodifications may be made to the shape of the disk, and the materialsused in constructions, without departing from the scope of thisinvention as set forth.

What is claimed is:
 1. An accessory for a grinder comprising a rotatabledisk-shaped tool having an axis of rotation and adapted to be mounted onan arbor of an angle grinder and being provided with a working zoneextending inwardly from the perimeter of the tool; rest means locatedradially inwardly of the working zone of the tool and displaced by afixed distance from the working zone along the line of the axis ofrotation of the tool and away from the grinder, characterized in thatthe working zone of the rotatable tool is provided with a plurality ofbristles capable of performing a cutting or abrading action when inrotational motion, the bristles projecting from the surface of theworking zone and the length of the bristles being such that a portion ofthe rest means can be contacted with a work surface while the tool isrotating with no cutting or abrading contact occurring between thebristles and the work surface and the disk-shaped tool is provided withat least one viewing aperture through the disk.
 2. An accessoryaccording to claim 1 in which the bristles are formed from metallicwire.
 3. An accessory according to claim 1 in which the bristles arelocated in a working zone extending from the outer perimeter of thedisk-shaped tool to a point that is up to two thirds of the distancefrom the perimeter to the axis of rotation.
 4. An accessory according toclaim 1 in which the bristles are located in a working zone extendingfrom the outer perimeter of the tool to a point that is up to one thirdof the distance from the perimeter to the axis of rotation.
 5. Anaccessory according to claim 1 in which the bristles are located in atleast two groups equally spaced around the working zone.
 6. An accessoryaccording to claim 1 in which the tool has a convex surface with theworking zone provided by an outer peripheral portion of the convexsurface of the disk and in which the rest means is provided by a portionof the convex surface of the disc located within the working zone.
 7. Agrinder comprising an accessory according to claim 1 in which the restmeans comprises an attached protrusion spinning with the accessory.
 8. Arotatable abrading tool according to claim 1 in which the rest meanscomprises a separate protrusion mounted on the tool.